Memory organization
Upcoming SlideShare
Loading in...5
×
 

 

Statistics

Views

Total Views
468
Views on SlideShare
468
Embed Views
0

Actions

Likes
1
Downloads
11
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Adobe PDF

Usage Rights

CC Attribution-NoDerivs LicenseCC Attribution-NoDerivs License

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

Memory organization Presentation Transcript

  • 1. Unit 4 - Memory Organization Abhineet Anand Computer Science and Engg. Department University of Petroleum and Energy Studies, Dehradun November 30, 2012 Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 1 / 19
  • 2. Outline 1 Introduction Memory Memory Hierarchy Memory Management System 2 Main Memory 3 Auxiliary Memory 4 Associative Memory 5 Cache Memory Characteristic of Cache Memory Associative Mapping Direct Mapping Set- Associative Mapping 6 Virtual Memory Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 2 / 19
  • 3. Memory The memory that communicates directly with CPU is called main memory. Devices that provides backup storage are called auxiliary memory. Only program and data currently needed by the processor resides in main memory. All other information is stored in auxiliary memory and transferred to main memory when needed. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 3 / 19
  • 4. Memory Hierarchy Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 4 / 19
  • 5. CPU Register - also known as Internal Processor Memory. The data or instruction which has to be executed are kept in these registers. The Cache Memory is employed in computer system to compensate for the speed differential between main memory access time and processor logic. The cache is used for storing segments of programs currently being executed in the CPU and temporary data frequently needed in the present calculations. By making program and data available at a rapid rate, it is possible to increase the performance rate of the computer. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 5 / 19
  • 6. Memory Management System Many operating system are designed to enable the CPU to process a number of independent programs concurrently - known as multiprogramming. Sometimes a program are too long to be accommodated in total space available in main memory. A program with its data normally resides in auxiliary memory. When the program or a segment of program is to be executed, it is transfered to main memory to be executed by the CPU. The part of the computer system that supervise the flow of information between auxiliary memory and main memory is called the memory management system. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 6 / 19
  • 7. Main Memory The principal technology used for main memory is based on semiconductor integrated circuit. The Integrated circuit chips are available in two possible operating modes: Static Dynamic The Static RAM consists essentially of internal flip-flop that store the binary information. The dynamic RAM stores the binary information in form of electronic charges that are applied to capacitors. The stored charge on the capacitor tend to discharge with time and the capacitors must be periodically recharged by refreshing the dynamic memory. The static RAM is easier to use and has shorter read and write cycles and used in cache. The dynamic RAMs are used for implementing the main memory. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 7 / 19
  • 8. Auxiliary Memory The Most common auxiliary memory devices used in computer system are magnetic disk and tapes. Other components used, but not as frequently, are magnetic drums, magnetic bubble memory, and optical disks. The average time required to reach a storage location in memory and obtain its contents is called the access time. In electromechanical devices with moving parts such as disks an tapes, the access time consists of seek time required to position the read-write head to a location and a transfer time required to transfer data to or from the devices. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 8 / 19
  • 9. Associative Memory An assembler program searches the symbol address table in order to extract the symbol’s binary equivalent. The number of accesses to memory depends on the location of the item and the efficiency of search algorithm. Many search algorithm have been developed to minimize the number of access while searching for an item in a random or sequential access memory. The time required to find an item stored in memory can be reduced considerably if stored data can be identified by the content of the data itself rather than an address. A memory unit accessed by content is called an associative memory or content addressable memory(CAM). Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 9 / 19
  • 10. Associative Memory This type of memory is accessed simultaneously and in parallel on the basis of data content rather then by specific address or location. When a word is written in an associative memory, no address is given. The memory is capable of finding an empty unused location to store the word. When a word is to be read from an associative memory, the content of the word, or part of the word, is specified. The memory locates all words which match the specified content and marks them for reading. An associative memory is more expensive than a random access memory, so are used in application where the search time is very critical and must be very short. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 10 / 19
  • 11. Cache Memory A typical computer program flows in a straight-line fashion with program loops and subroutine calls encountered frequently. Analysis of a large number of typical programs has been shown that the reference to memory at any given interval of time tend to be confined within a few localized areas in memory. This phenomenon is known as the property of locality of reference. If the active portions of the program and data are placed in a fast small memory, the average memory access time can be reduced, thus reducing the total execution time of program. Such memory is known as Cache memory. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 11 / 19
  • 12. Cache Memory The Performance of cache memory is frequently measured in terms of a quantity called hit ratio. When the CPU refers to memory and finds the word in cache, it is said to produce a hit. If the word is not found in cache, it is in main memory and it counts as a miss. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 12 / 19
  • 13. Characteristic of Cache Memory The basic characteristic of cache memory is its fast access time. The transformation of data from main memory to cache memory is referred to as a mapping process. Three types of mapping procedures are: Associative Mapping Direct Mapping Set-associative Mapping Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 13 / 19
  • 14. Associative Mapping The fastest and most flexible cache organization uses an associative memory. The associative memory stores both the address and content (data) of the memory word. If the address is found corresponding data is read otherwise main memory is accessed for the word. It is expensive compared to random-access memories because of the added logic associated with each cell. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 14 / 19
  • 15. Associative Mapping Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 15 / 19
  • 16. Direct Mapping The n-bit memory address is divided into two Fields: k-bits for the index field and n-k bits for the tag field. The direct mapping cache organization uses the n-bit address to access the main memory and the k-bit index to access the cache. Each word in cache consists of the data word and its associated tag. When a new word is first brought into the cache, the tag bits are stored alongside the data bits. When the CPU generates a memory request, the index field is used for the address to access the cache. The tag field of the CPU address is compared with the tag in the word read from cache. If the two tags match, there is a hit and the required word is read from cache otherwise it is read from main memory. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 16 / 19
  • 17. Set- Associative Mapping In Direct mapping, every time a miss occurs, an entire block of words must be transfered from main memory to cache memory. Another disadvantage of direct mapping is that two words with the same index in their address but with different tag values cannot reside in cache memory at same time. A third type of cache organization, called set-associative mapping, in which each word of cache can store two or more words of memory under the same index address. Each data word is stored together with its tag and the number of tag-data items in one word of cache is said to from a set. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 17 / 19
  • 18. Virtual Memory In a memory hierarchy system, program and data are first stored in auxiliary memory. Portion of a program or data are brought into main memory as they are needed by the CPU. Virtual Memory is a concept used in some large computer systems that permit the user to construct programs as though a large memory space were available, equal to the totality of auxiliary memory. A virtual memory system provides a mechanism for translating program-generated addresses into correct main memory locations. An address used by a programmer will be called a virtual address, and set of such addresses the address space. An address in main memory is called a location or physical address and the set of such addresses is called memory space. Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 18 / 19
  • 19. THANK YOU Abhineet Anand (UPES, Dehradun) Unit 4 - Memory Organization November 30, 2012 19 / 19